System of aeration



Patented July 3l, 1945 UNITED STATES PATENT OFFICE SYSTEM AERATIONChester F. Proudman, New Canaan, Conn.

Application February 14, 1939, Serial No. 256,276

` 3 Claims. (Cl. 2108) This invention relates to apparatus and methodsused in the activated sludge treatment of sewage and analogous liquids.

In the customary activated sludge treatment of sewage, the raw sewage isinitially passed over settling beds or through screening apparatus toremove the heavier and more solid materials. The liquid component, orprimary eiiluent, ilows into open tanks where it is mixed with activatedsludge for the purpose of "seeding or starting the action of thebacteria. In order to supply oxygen and propagate the aerobic bacteria,air is caused to bubble through the liquid and is dispersed to theVatmosphere immediately above the tank. Various devices to agitate theliquid and secure better aeration are used.` The action oi the bacteriapuriies the liquid in the tank `and with the proper conditions avigorous growth of the aerobic bacteria is obtained.

From the aerating tank the liquid, containing the activated sludge,passes to a settling tank. From this tank the liquid in more or lesspuriied condition, is drawn off. VA portion-of the sediment or activatedsludge is mixed with the incoming `primary eiiluent for seeding purposesand the remainder goes to the digesters with the initialscreenings'taken from the system.

A major source of trouble inthe customary operation of activated sludgesystems is the bulking of the sludge, which condition interieres withproper aeration.

The quantity of air required in operating the customary system isapproximately two cubic feet of air per gallon of liquid treated and thefurnishing of this quantity of air is a large item of expense. It isestimated that only ten percent of the available oxygen in the air isutilized by present methods, the remaining ninety percent being wasted.

This invention is particularly directed to the intermediate treatment ofthe primary eiiluent` betrifft-n the primary elliuent channel and thesettling tanks. l

The general objects of this invention are to provide apparatusandmethods which will increase the eiliciency of the purifying plant,reduce the cost of operation and provide better control.

A principal object of this invention is the provision of closed tanks toenable the same air to be passed through til` liquid in successive tanksand thereby obtain adc.;onal aerotion from a given volume of air.

A further object of this invention is to provide covered tanks which maybe maintained underV pressure to secure a higher percentage of dissolvedoxygen in the liquid undergoing treatment.

A further object of this invention is kto provide covered tanks notrequiring internal moving parts or objectionable sludge accumulatingbailles, jogs or partitions to secure the necessary aeration.

A further object of this invention is to provide denite control of thevolume of liquid to be treated so that proper purication is effectedunder all conditions.

A further object of Vthis invention is to prevent short circuiting ofthe tanks whereby portions of the liquid may not receive proper aerationor bacterial action.

A further object of this invention is to reduce and practicallyeliminate bulking of the activated sludge.

A further object of this invention is to supply the proper quantity ofair to the tanks in accordance with the biochemical oxygen demand asdetermined by tests for dissolved oxygen.

A further object of this invention is the provision for culture controlin separate tanks, whereby the final activated sludge obtained will bein the mostl vigorous condition and best adapted for seeding purposes.

A further object of this invention is the provision of two or moreseries of tanks to secure for a plurality of connected tanks, each underindividual control and each progressively increasing the activation orvigor of the bacterial content of the sludge entrained with the liquidpassing through said tanks.

A further objectof this invention is the provision of automatic valves,controlled by a com ventional timing mechanism, to effect batch controlof the tanks. v

To these and other ends the characteristic features and advantages of myimprovement will more fully appear in the following description and theaccompanying drawings in illustration thereof.

In the drawingsy in which like reference numerals designate like partsFig. l is a general plan view of .the parts of an aerating and purifyingplant coming within the scope of .this invention.

Fig. 2 is a side elevation, partly broken away, of the apparatus of Fig.1.

Fig. 3 is a vertical cross section through one of the intermediate tanksequipped with autc matic control.

Fig. e is an automatic solenoid operated valve yto be used in connectionwith this invention.

Fig. 5 is a spring loaded pressure relief valve adapted to be used inconnection with this invention.

Referring to Fig. 1, reference numeral I designates a portion of achannel in which the primary effluent from the primary settling beds orscreening apparatus is received. I I is a Weir or mixing chamberadjacent to and connected with the channel I0 and into which theactivated sludge used for seeding purposes is conveyed through the pipe10. i3 is the inlet pipe carrying the primary eiiluent plus theactivated sludge into the first tank I5. A valve i4 controls the flowthrough the pipe i3. The tank I is provided with the side walls i6, aclosed top I1 and a bottom I3, preferably hopperlike in shape.

At the bottom of the tank I5 is the opening 2I connecting with the exitpipe 2i which is provided with the valve 22. The pipe 2| connects thetank l5 to the tank 39, the next successive tank in the series.

lit will be understood that the effluent channel and the several tanksmay be arranged to meet specific plant conditions. For purposes ofdescription the foundation 5 having the walls 6 and the subfloors 1 and8 are shown as housing and supporting the channel lll and the tanks I5,3U, 45 and till which comprise the apparatus of the invention.

The tank 3l) is similar to the tank I5 and comprises the side walls 3l,the top 32 and the bottom 33. At the bottom of the tank 30 is .theopening 35 connecting with the exit pipe 36 having the valve 31. Thepipe 36 connects the tank 39 to the tank 45, `the next successive tankin the series.

The tank 45 is similar .to the tanks I5 and 38 and comprises the sidewalls 46, the top 41 and the bottom 48. At the bottom of 'the tank 45 isthe opening 5i) connecting with the exit pipe 5I having the valve 52 andconnecting the tank 45 to the settling tank, or basin, 60.

It will be understood that the tank tops I1, 32 and 41 are removable foraccess to the inside of the tanks.

The settling basin G may be of conventional construction and may be openat the top. It is provided with a pipe 6I, to withdraw purified liquid,and a hopper bottom G2 into which the activated sludge settles. The tank60 has a valved drain 63. The bottom outlet 64 connects through thedischarge pipe 35, and valve 56, with the sludge pump 61. The outlet 68of the sludge pump 61 is divided, one branch, the pipe 10 dischargesactivated sludge into the mixing Weir II. The other branch, the pipe 69,leads to the screen apparatus or digesters and disposes of the surplusactivated sludge, which is not used for Seeding purposes.'

For the purpose of supplying air to the tanks a source of compressed air15, normally consisting of an air compressor and a storage tank, isprovided. This compressor may be driven in any convenient manner. Oneair compressor, as at 15, will supply air for a number of tanks and itwill be understood that suitable pipe connections will be made toaccomplish this.

The pipe 16 having the valve 14 connects the source of compressed air 15with the tank I5. The air pipe 16 has a leg 11 extending downwardly into`the tank I5. At the end of the leg 11, and in proximity to the bottomof the tank I5, is a. conventional porous block 18 as shown through thecut away section of tank 30 in Fig, 2 and in Fig. 3.

The porous blocks 18 are attached to .the ends of the legs 11 in such a.manner as .to cause the air forced through the legs to diffuse throughthe blocks and in operation bubble upwardly through the liquid in minutebubbles. From the spaceVor air dome 9I, at the top of the tank I5 theair pipe 19 having a valve 80 connects with a leg 11 which extendsdownwardly into the tank 30. The leg 11 in the tank 30 carries a similardiffusion block 18 as described in connection with Itank I5. From thespace, or air dome 92; at the top of the tank 30, the air pipe 8I havinga valve 82 connects with a leg 11 which extends downwardly into the tank45. The leg 11 in the tank carries a similar diffusion block 18 asdescribed in connection with tanks I5 and 30. From the space, or airdome 93, near the top of tank 45 is connected an exhaust pipe 83 havingthe valve 34. The pipe 83 exhausts through .the valve 84 into theatmosphere.

The openings in the tank tops I1, 32 and 41, for the passage of the legs11 into the tanks, are sealed about the legs 11 to hold the pressurewithin the tanks.

The method of use of the apparatus shown and described is as follows, itbeing understood that an initial charge of activated sludge is placed inthe hopper 62 of the tank 60.

Primary eiiluent passes from the channel I8 into the Weir I I. Activatedsludge is withdrawn from the tank 60, and by means of the sludge pump 61and the pipe 10, a suitable quantity for seeding purposes is conveyed tothe Weir I I and mixes with the effluent passing through the Weir. Themixture of effluent and activated sludge flows through the pipe I3 andthe valve I4 into the tank I5, and reaches the liquid level of theapparatus as shown by the dot and dash line 90 in Fig. 2. The mixture ofprimary effluent and activated sludge will pass through the pipe 2l, thevalve 22 and into the tank 30 until it reaches the liquid level line 90.In starting the operation of the plant the valve 31 will be closed andtherefore the tank 45 will remain empty. Compressed air from the sourceis now fed through the pipe 15, the leg 11 and the diffusion block 18into the tank I5 and, as described above, will rise through the liquidin the tank I5 to the air dome or space 9I above the liquid level in thetank.

When an air pressure is built up sufficiently in the dome 9I of the tankI5 the air will be forced through the pipe 19, the valve 80 and downthrough the leg 11 in the tank 30 and, as described above, will bubbleupwardly from the diffusion block 18 and through the liquid in the tank30, accumulating in the space or air dome 92 above' the liquid in thetank 30. From the air dome 92 the air will be forced through the pipe8|, the valve 82, and the leg 11 into the tank 45 and upwardly throughthe tank 45 into the upper space or air dome 93 in the top of the tank45, and then outwardly through the exhaust pipe 83 and open valve 84 tothe atmosphere. In starting, the apparatus is run with the two tanks fora period until the bacterial action has secured the desired purificationof the liquid in the tanks I5 and 30.

The air valve 14 in the pipe 18 is now closed. The valves 22, 31, 52 and66 are opened, the sludge pump 61 is started and activated sludge is fedfrom the hopper 62 of the tank E0, through the pipes 65 and 10 to themixing Weir Il. The valve I4 is opened and primary eiliuent mixed with`activated `sludge --is -tothe liquid levelline 90.

ratus may be considered tobe finished.

fed through lthe pipe ,-JI 3 having a volume. equaljtov tank yI5,will'result with'liquid `up in the three tanks beingl filled After thenew batch has .beenV takenl into the sludge duringfthe process, and thus`secure .a contankfl the sludge pump yI1 kis stopped, the valves66,114,122, 31 and 52 are'closed and theair valve 14 opened. l f l. 1 uIt will nowbe lnotedthatthe tank I5 i's1lled with primary'eilluent in'anunpurifiedstate mixed with. activated sludge, while tanks4 43l?!.andf'r45 puriiied liquid `mixed with are fiilledwith a moreactivatedisludge.. Y,

The .air supply'is passedithrough: the ,tanks as above described andthetreatment .is l continued for the desiredlength yof time so that theliquid inl. tank 45 will become puried to'fthe point desired.

At this point the operating cycle ofrtheapparatus may be considered tobe completely started.

The air valve 1`4.is now closed,l and the valves 66', I4, 22,131 and52..areopened. Thevsludge pump61 is started and a, newxbatch of'primaryeffluent plus activatedsludge ilowsainto the -rtank lI5 from the.mixingweir II.. Thedischarge; end

53 of .the pipe. 5I is. lower. thanthie level; of 'the A liquid in thetank 45 and lower than'zthefpipe I3 v entering the tank I5. Therefore,whenthe valve' .52. is opened the liquid will. flow-out. of y.the tank'.45 into, the tankv, and this inturnwillcause liquid to flow into thetank 45 from the tank 30, thereby loweringthe liquid level' in' the tank30.

The lower liquid level in the tank @will in: turn cause liquidto -flowfromthetank .I 5 into-the tank and the new batchfentering lthetank .I5will take the place yof, the, liquid which passes-into the tank. .mi Thevalves 65, 14, 2231 `and 5,2 are now-closed, the air valve V14isopenedand vair -is passed'as' ldescribed .through the, liquid .in thetanks fora period to obtain the |desired puri'catlion injthe tank i. ,IJ j A1 l l; At this point the operating cyclexof theappa- To-starta-newcycle,the air valve 14 yis 4again closed, the valves 66, I4, 22, 31and 52 are opened and a new batch of elluent` is fed into tank |15,while a purified batch of liquid, havingthe activated sludge entrainedtherewith, ywill pass intov the settling tank 60.

From the description given it will be noted that l successive batches ofprimary effluent and activated sludge are fed to the first tank of theseries and batches of puried liquid and activated sludge of similarvolume are at the Sametime withdrawn from the last tank of the series.The

batches being progressively purified as they pass` through successivetanks in the series.

air, this diierence being due -to the passage of the air through the rsttank.' Forfthe same reason the air passing through the third tank isalso conditioned as described. The term gaseous mixture as used hereinrefers toand denes airvin its normal stateand also air which hasy been"conditioned or altered y vby passage through a body of eilluent.

ldition of .the sludge in the settling .tankswhich From lexperience ithas-.been found thatv the liquid is practically vin a purified statewhen it "enters the last tank of theseries and thusr the 4work-0f this-lnalltank isVr directlychiefly to invigorating the ybacterial contentof the sludge. l

f Inorder to secure a continuous ilo'w of primary effluentv fromthemixing channel, and acontinuousr flow ofJ purified liquid into thesettling tanksduplicate apparatus `may be provided as showninplan-viewinFig. l. During the period linl which the liquid in one series of tanksis ,un- '-dergoing treatment, the primary eluentwill be owin'g into thefirst Vtankof the other series and puriiiedV liquid will be flowing-outofthe last tank. This condition alternates between theseries and resultsin* a continuous flow from4 the `mixing channel to the settling tanks.

k, As described,fitl will be Inoted that thepressure whichi will buildup in the airdome 92 inthe top ,of` the tank 30 need bejustsuicient.toovercome thepressure due to vthe head of liquid in tankytin v'order to secure the i passage of. air throughthe `pipe 8| and the'leg :Hin tank 45. Similarly, in gorder to secure aflowfoffair throughtheltank 30 from the air dome `92| in.the.top of thetank I5 the pressurein tank zl5inustfovercomethe presn sure due to the head ofliquidintankfiill plus pressure existing on top of theliquid. f If,iorexample, the liquid; head in the tanks is.l about ten feet, thepressure in the air dome 92.willbe approximately ve pounds iper squarevinch andA the pressure in the'air .dome 9|.will be approximatelytenpounds .per square -inch.y .Ifthe valve 8451s open to the atmosphere asabove described it is obvious there Will be atmospheric .pressure in theair dome 93 in the top'of the tank'45. L.

Since-the quantity ofgas .which ,Irlafybedis` ventional design, like.that shown in Fig. 5 may be substituted Afior .theplain valve 84"and'the loading adjusted to give any desired 'pressure'in' the air dome 93at the top of the tank 45. Any

increase in the pressure in the tank 45 willfof course, require` andresult in correspondingly increased pressure in the tanks 30 and I5.

Should itbe desired tomaintain only the first tank of the series underhigher pressure this result can ,be AObtained by substituting a loadedvalve, like that of Fig. 5, for the valve 8U between the rst' and secondtanks of the series. vSubstituting lthevalve 82 with a loaded valvewill-increase thepressure in the first two tanks of the series.

In yorder `to cut down'the operating labor and to render the apparatuspractically automatic the diiierent components than the original normalvalves 14, I4, 22, 31, 52 and 66 may be replaced with electricallyoperated solenoid valves of conventional type as shown in Fig. fi, orreplaced by the equivalent ofy such a valve. If such automatic valvesare used, they will be controlled by means of aconventional timingapparatus which will open and close the valves periodically as requiredto carry out the steps of the method. The sludgepump 61 will, of course,be controlled by the same timing apparatus.

Fig.. 3 shows 'an aeratng tank equippedwith automatic control. Theliquid supplyv line 2| and the liquid discharge line 36 being eachprovided with an electrically controlled valve |03. The air exhaust line8| is shown as provided with a loaded relief valve |05. In this figurethe air bubbles are shown as passing upwardly through the liquid |0|.

If desired, the air admission line 19 may enter the tank near its lowerend as shown by broken lines at |0'|.

The solenoid operated valve |03 shown in Fig. 4 is operated by reversingthe direction of the current through the coil |04, in the well knownmanner.

'I'he loaded relief valve |05 shown in Fig. 5 is adjusted by varying thecompressionA of the spring |06.

It will be understood that two or any greater number of tanks may beused in one series. The quantity of air forced through the tanks varyingwith the total volume ofA liquid being treated in the series. s

It will be understood that the pipe sizes and valve openings areadjusted to permit the entryv of a new batch into the tank I5 within thedesired period of time.

It will be understood that the purified liquid is drawn oil? from thesettling tank 60 through the outlet 6| to permit successive batches tobe emptied into the tank 60.

If desired, in transferring batches, the valve I4 may be kept closed andthe air Valves 80, 82 and 84 may also be closed, and the air valve |14opened. This will result in building up pressure in the tank I5 andserve to rapidly force the liquid in this tank through the pipe 2| intothe tank 30. The entry of this batch of liquid into the tank 30 will inturn force liquid into the tanks 45 and 60, to the end that the newbatch may be placed in the apparatus in a short time.

It will be understood that pipe connections and valves, in addition tothose shown, may be pro vided to enable any one of the tanks in a seriesto be by-passed for cleaning, repair or other purpose.

I claim:

1. Apparatus to treat sewage eilluent comprising a primary eiiluentchannel; a series of closed 'aerating tanks to hold batches of ellluentfor treatment; a settling basin for activated sludge and an outlet fromsaid basin forfpuriled liquid; a pump and pipe means to mix activatedsludge from said basin with the eilluent in said channel; a valvedpassage between said channel and therst tank; a valved passage leadingfrom the bottom of each tank to a point near the top of the next tank inthe series; a valved passage leading from the `bottom of the last tankto a point near the top of said basin; said passages being closed toretain isolated batches of effluent,

for an aeration and reaction period, in each of said tanks and saidpassages being opened to provide for the passage of each batch of eluentfrom each tank to the successive tank in the series and nally to saidbasin; and aerating means comprising air pipes between and within thetanks to provide for the passage of air during the reaction periods,through the effluent isolated in the rst tank and thereafterprogressively through the elliuent isolated in each of the successivetanks in the series.

2. An apparatus to purify sewage effluent comprising a series of closedpressure holding aerating tanks; valved pipe connections between thebottom of one tank and the top of the next succeeding tank in theseries: said valves being closedto isolate for treatment a batch ofeffluent in veach tank of said series; said valves being Opened and saidpipe connections being arranged to provide passage for the movement ofeach batch of eilluent progressively through said series 0f tanks andmeans to feed air progressively through the eflluent treated ineachtank.

3. An apparatus to purify sewage effluent comprising a series of closedpressure holding tanks; valved pipe connections between the bottom ofone tank and the top of the next succeeding tank in the series: saidvalves being closed to isolate for treatment a batch of ell'luent ineach tank of said series; said valves being opened and said :pipeconnections being arranged to provide passage for the movement of eachbatch of ellluent progressively through said series of tanks and meansto feed a gaseous mixture, of altered composion, through the eiliuentisolated in each tan CHESTER F. PROUDMAN.

